CHEMICAL CONSTITUTION OF VARIOUS SR-IR-O PHASES

The compositions of several phases in the Sr-Ir-O system have been reported in the past thirty years, and the single crystal structures of three of these have now been determined. The formulation for one of these phases, namely the body-centered cubic, has been assigned different ratios of strontium, iridium and oxygen by various workers, which has led to some confusion as to its exact chemical composition. To clarify this situation, a study of the composition of the different Sr-Ir-O phases was carried out by electron microprobe analysis using a Kevex quantum energy dispersive detector, which is readily capable of detecting the K(alpha) X-ray emission from oxygen along with that from heavier elements. Reference standards of pure IrO2, SiO2 (quartz), fused SrCl2 and SrCO3 were used for calibration of Ir, O, Cl and Sr contents respectively. In addition, the Sr to Ir ratio was determined by using known standards such as the well-characterized monoclinic and orthorhombic (high-pressure) forms of SrIrO3, and Sr2IrO4. The analysis of the body-centered cubic Sr-Ir-O phase indicates a chemical formula of Sr0.79IrO2.8Cl0.07. The trace of chlorine may be necessary to stabilize this structural form of the compound.